Simple this: if you have a bike without rack mounts on the seat stays, and you want to fit a rack, pop off your standard seat collar and fit this Rack Lock from Salsa instead.
Obviously it'll still do the job of keeping your seatpost in the right place but welded on to the rear is a barrel with both ends tapped out with an M5 thread, so you can attach your rack to it. That means the pinch bolt is round the front, which keeps it out of the way of mucky spray from the rear wheel (if you don't have mudguards) which is an added bonus.
What about the bottom of your rack? Well, if you have eyelets then you're sorted, otherwise you'll need an assortment of P-clips and swear words.
Basically this is an ideal solution for getting a rack on a bike that has mudguard eyelets at the rear dropout, but no rack mounts; that's quite a lot of bikes these days. I've used it with a low-profile Tortec Velocity rack and it's done the job with zero fuss. There's not really a lot more to say about it: if that's your problem, this is the solution. It's available in 30.0, 32.0 and 35.0mm diameters for different frames.
Neat way to fit a rack to a frame without top rack mounts
road.cc test report
Make and model: Salsa Rack Lock seat collar
Size tested: Black, 30.0mm
Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
Rack-Locks are one part form, two parts function. Sure, they still look great and do a great job of keeping your seatpost in place, but they also provide a mounting position for the front struts of a rack
Tell us some more about the technical aspects of the product?
Welded on rack attachment points
34mm-wide rack mount threaded for M5 bolts
Stainless steel pivot and bolt
Black or Silver anodized with laser-etched logo
30.0, 32.0 and 35.0mm
Tell us how the product performed overall when used for its designed purpose
About as well as possible
Tell us what you particularly liked about the product
Tell us what you particularly disliked about the product
Did you enjoy using the product? Yes
Would you consider buying the product? Yes
Would you recommend the product to a friend? Yes
About the tester
I usually ride: whatever I'm testing... My best bike is: Genesis Equilibrium with SRAM Apex
I've been riding for: 10-20 years I ride: Every day I would class myself as: Experienced
I regularly do the following types of riding: commuting, sportives, general fitness riding, fixed/singlespeed, mtb, Mountain Bike Bog Snorkelling, track